Resolution of a Configurationally Stable Hetero[4]helicene.

We have developed an efficient chemical resolution of racemic hydroxy substituted dithia-aza[4]helicenes (DTA[4]H) using enantiopure acids as resolving agents. The better diastereomeric separation was achieved on esters prepared with (1)-(-)-camphanic acid. Subsequent simple manipulations produced highly optically pure (≥ 99% enantiomeric excess) () and ()- in good yields. The role of the position where the chiral auxiliary is inserted (- vs. ) and the structure of the enantiopure acid used on successful resolution are discussed.